Final answer:
The R44 and R46 classes of New York City Subway cars originally used rollsigns for side signage, which have since been replaced by electronic displays.
Step-by-step explanation:
The side signs on a R44 and R46 refer to the signage on the New York City Subway rolling stock. The R44s and R46s are a class of subway cars that were manufactured in the 1970s.
The signage system used in these models was originally rollsigns, which are mechanical signs that display the train's destination and route information via a rolling mechanism that switches between pre-printed options. Over time, these rollsigns were replaced with modern electronic displays that provide more flexibility and are easier to update.